AB1383 QUANTIFICATION OF THE PD SIGNAL BY COMPUTER ANALYSIS OF STATIC IMAGES: INTRA-OBSERVER, INTRA-PATIENT AND SENSITIVITY TO CHANGE VALIDATION.
Authors: C. Guillén-Astete, Á. Andreu-Suárez, M. Tortosa-Cabañas
Journal: Annals of the Rheumatic Diseases (2022)

Background The computerized assessment of ultrasound images is an alternative to the dichotomous subjective assessment often used in the study of entheses. Previously, our group has demonstrated its usefulness in assessing greyscale images; however, the evaluation of enthesial hyperemia using this technique remains a pending task. Objectives -To determine the intra-observer and intra-patient variability of the hyperemia study using computer analysis of static images. Methods Patients with a diagnosis of known spondyloarthritis and ultrasound enthesitis of the Achilles tendon -according to EULAR criteria (detection of hyperemia by power Doppler (PD) signal within 2mm of the cortex)- were selected. Longitudinal medial, central and lateral image sections were obtained. Hyperemia was assessed by PD signal detection, and the images with the highest signal intensity were recorded, maintaining the same doppler gain and PRF settings for each subject. For image analysis, recordings were coded and randomized so that the analyst did not know to which patient a given section corresponded. Intra-patient validity was assessed by comparing the results of sections from the same patient with each other at two different times. Intra-observer validity was evaluated by subjecting the same image to two computer analyses at different times. Finally, validation of sensitivity to change was performed by successive measurements. The software used was ImageJ 1.53e (NIH, USA). Results Images of 12 patients with Achilles enthesitis were included: 6 patients with SpA-nRx, four patients with PsA, and two patients with SpA-Rx. On intra-patient evaluation, significant differences in PD signal intensity were detected between medial, lateral, and central sections. In all cases, the measurement obtained in the central section was the highest (Friedman 15.500 P=.000; medial-central -1.500, P=.001; lateral-central -1.250, P=.007). The coefficient of variation in the first and second determinations without considering the sign of the variation was: 4.2% SD 5.5%. In the intra-observer evaluation of the PD signal evaluations at the central cut-off, the mean coefficient of variation, without considering the sign, was: 9.1% SD 7.2%. In assessing sensitivity to change, patients with 6-month ultrasound studies were grouped into those who maintained treatment and those who eventually discontinued treatment due to therapeutic failure. In the seven patients who maintained treatment, the mean change in hyperemic areas was -94.3% SD 4.4%, while in the five patients who discontinued treatment, it was -65.4% SD 6.3% (p=.000). Figure 1. Evaluation of the PD signal. Conclusion Computer analysis of static Achilles tendon images conforms to the same ultrasound image acquisition recommendations. In addition, it demonstrates excellent intra-patient and inter-observer variability and sensitivity to change, at least when correlated with therapeutic success or failure from a clinical perspective. Disclosure of Interests Carlos Guillén-Astete Speakers bureau: Novartis, Janssen, Abbvie, Grunenthal, UCB, Gebro, Paid instructor for: Roche, Novartis, Janssen, Esteve, Menarini, Consultant of: Janssen, Novartis, Roche, Grant/research support from: Pfizer, Grunenthal, Gebro, Novartis, África Andreu-Suárez: None declared, Marina Tortosa-Cabañas: None declared